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HXr and Fuel Levels

Postby Bayou Bert » Fri May 15, 2015 8:09 pm

I am finally at the point of doing fuel flow testing and tank calibration.
I have the resistor floats from Vans. I hooked the up to Analog 1 and 2 to the EFIS per instructions.
I went in and completed all the setting, pull up resistor, etc per instructions.
The fuel levels were showing both as full with tanks empty. I had tested the floats with ohmmeter
before wing install and they were like 235 ohms empty and around 30 ohms full.
I talked to someone at GRT today and after some hesitation they told me to go from integer to decimal.
Now I have fuel bars that are about 1/8" off the bottom and each read 2.
Is there something else I need to do or is that just what my floats read when empty?
I didn't have time to put fuel in and see what happens.

Thanks
Bert
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Re: HXr and Fuel Levels

Postby Bobturner » Sat May 16, 2015 1:17 am

Are you following the instructions? They are pretty well written, but sometimes hard to find. Go to the GRT web site, then:
<Support> <documentation> <EIS and Sensors> <Float type senders with the Horizon>
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Re: HXr and Fuel Levels

Postby Bayou Bert » Sat May 16, 2015 10:44 am

Yep, printed and in hand. Tried playing with the offset, and can increase the number but not reduce.

Bert
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Re: HXr and Fuel Levels

Postby Bobturner » Sat May 16, 2015 11:13 pm

You haven't put any gas in yet? Then you cannot use the internal calibration program without "faking" it.
I think you want reverse sensing. Set offset to zero per instructions. Note the signal level (they call this the probe signal) at empty. Fake the gauge into thinkng it's full by putting a 30 ohm resistor across the float gauge. Record the signal level and call it 30 gal or whatever full is. Now follow thru the instructions and enter these two pairs of numbers into the calibration columns, and save. Zero should then be sero.
When you get the chance make more measurements as you slowly fill the tanks. I did it every 5 gallons, and the results are amazingly accurate.
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Re: HXr and Fuel Levels

Postby Bayou Bert » Mon May 18, 2015 5:19 pm

Thanks Bob, kinda hacked at the moment.
Present position, have done two fuel flow test, still need to do nose down.
Tank settings are per GRT except for integer/decimal, now on decimal, not per written instructions.
I checked ohm readings at empty, both in the 240/245 range. Put 3.5 gallons in right tank.
No movement of level on EFIS, but ohms declined to 180, as designed to do.
Completely out of ideas. I did not understand what you posted above.

Bert
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Re: HXr and Fuel Levels

Postby Bobturner » Mon May 18, 2015 9:55 pm

Let me try again. It sounds to me like you have not completed the set up calibration as described on page 8, step 6, of the above referenced instructions. And you cannot since you haven't taken data with various levels of fuel. I meant to suggest you can fake the full reading since you said the float read about 30 ohms when fully "up". So put a 30 ohm resistor across the float terminals (really you'll have 30 ohms and 240 ohms in parallel, = 26.5 ohms, so 33 ohms is a bit better) and see what the display is indicating (if it is less than 2, put "reverse" into the set up on page 7, table 3.1). Let's say the indication on the EFIS with the 33 ohm resistor in place is 9 gal. Now go to the worksheet 2 on page 9, write in the pairs (2, 0), (9, 15) for (probe, fuel level) if in fact the EFIS read 2 when empty, and 9 with the 33 ohm resistor in place, and the tank is designed to hold 15 gallons when full. Now transfer these numbers into the calibration table described on page 8, step 6, and save the whole thing. Empty should now read zero.
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Re: HXr and Fuel Levels

Postby Bayou Bert » Tue May 19, 2015 12:23 am

Thanks Bob, I sure appreciate the help. I have not tried the calibration. I could not see how I could tell if the float moves off the bottom, or stops moving at the top if the green level bar is already at the top.
How about the numbers over the bars, both either 19 or 20 with tanks empty right now.
Even with green bars at the top, will the numbers start climbing when the float moves off the bottom?
If that's the case then I can do the calibration and fill in the little log in the EFIS.

Thanks
Bert
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Re: HXr and Fuel Levels

Postby walkman » Sun Apr 22, 2018 9:56 pm

Does anyone know where this documentation now resides?

It surely is no longer in the above referenced location and every other reference I can find in the "documentation" (incomplete and lacking at best) is a broken link.

Stunned at the utter shambles of the documentation for a product that has been GA for 6 years!!!
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Re: HXr and Fuel Levels

Postby GRT_Jeff » Tue Apr 24, 2018 12:45 am

The Horizon / Analog Input / Calibration Table version of the document is present but doesn't appear to be linked from any page:

Calibrating Resistive Float-Type Fuel Senders with the Horizon EFIS
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